This invention relates to a method of filling a liquid crystal device with a liquid crystal.
Vacuum filling method is a known method for filling a space between a pair of substrates with a liquid crystal to manufacture a liquid crystal device. In this prior art method, the liquid crystal device is disposed together with the liquid crystal in a vaccum chamber at a vacuum, and then, after the inlet of the device is dipped in the liquid crystal, the pressure is elevated so that the liquid crystal enters the liquid crystal device. One type of this method is described in Japanese application No. sho 60-175192.
However, there are several shortcomings associated with this method. The inlet of the liquid crystal device is somewhat narrow so that the pressure in the liquid crystal device can not be lowered rapidly. Because of this, the liquid crystal device is subjected to the differential pressure between the inside and the outside of the liquid crystal device when the vacuum chamber is evacuated, and therefore tend to be deformed due to the undesirable pressure.
To comply with the shortcoming, it is proposed to mate a pair of substrates firmly to bear the differential pressure and maintain the distance between substrates with two or more types of spacers arranged therein. Nevertheless, in some instances the device may be destroyed due to a transient force of about 1 kg.cm.sup.2 which arises during evacuation.
Furthermore, the filling process is generally carried out in a particular phase of liquid crystal. A ferroelectric liquid crystal exhibits its phase transition as the temperature varies, e.g. Cry phase .rarw..fwdarw. Smc phase .rarw..fwdarw. SmA phase .rarw..fwdarw. Iso phase. The phase transition is observed also with a blended liquid crystal. An Iso (isotropic) phase is suitable for the filling process because of its low viscousity. An example of the method is described in Japanese Patent Application No. sho 60-175192.
However, when a blended liquid crystal material composed of several constituent liquid crystals is used, a particular liquid crystal of the constituents tends to enter first so that the liquid crystal material having entered into the device becomes different from the prescribed composition. Having carefully investigated the phenomena, the inventors found that the transition temperature of the blended liquid crystal is not observed clear at a certain defenite temperature and a mixed phase seems to appear between the constituents due to differential transition temperatures of the constituent liquid crystals. In other word, it may happen during filling process that a constituent liquid crystal is of Iso phase while another constituent liquid crystal remains in Smc phase.